1. Field of the Invention
The present invention relates, in general, to methods of tapering bristles for toothbrushes and toothbrushes having bristles manufactured using the methods. More particularly, the invention related to a method of tapering bristles for anchor-less toothbrushes and a anchor-less toothbrush which has bristles manufactured using the method.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
In conventional methods of manufacturing toothbrushes having tapered bristles, a bundle of bristles, each having an end point from 0.16 to 0.2 mm in diameter, is cut to a predetermined length. Thereafter, the end points of the bristles are hydrolyzed by an alkali chemical or strong acid chemical, thus being tapered. Subsequently, the bristles are washed in water and dried. The bristles are thereafter folded in half and set in holes, formed in a head part of a toothbrush body, using anchors.
Recently, toothbrushes have followed trends, so that various bristle setting patterns have been required. Furthermore, according to an increase in the size of a bundle of bristles, it has been difficult to set bristles using a conventional bristle setting machine and to fasten bristles with an anchor.
Three methods of manufacturing an anchor-less toothbrush are as follows.
First, as a method used by Coronet Co., Ltd. of Germany, bristles are set in a mold and, thereafter, resin is injected into the mold, thus integrating the bristles with a toothbrush body.
Second, as a method used the Oral-B company of U.S.A, bristles are set in a mold brush plate and, thereafter, the head insert having bristles is placed in a mold. Subsequently, resin is injected into the mold, thus fastening the bristles to a toothbrush body.
Third, as a method used the Boucherie company of Belgium which uses a bundle of bristles having a predetermined length, unlike other companies which use a spooled filament as a bristle. Bristles are set in a head insert made of plastic and, thereafter, the head insert is seated into a head insert seat formed in a head part of a toothbrush body. Subsequently, the head insert is bonded to the toothbrush body by ultrasonic waves.
The above-mentioned methods can reliably fasten bristles to a toothbrush body without anchor. However, the equipment is very expensive, and productivity is relatively low. Moreover, because a mold, a bristle setting machine and an injection molding machine are integrated together, it is very difficult to change the setting pattern of bristles.
However, toothbrushes manufactured by the above-mentioned methods can realize various bristle setting patterns. Thus, the appearance is superior. As well, the bristle setting pattern can freely be designed to match the tooth structure of every race. Therefore, toothbrushes manufactured by the above-mentioned methods have been popular among consumers.
In the toothbrushes manufactured by the above-mentioned methods, to realize various bristle setting patterns, the volume of a bundle of bristles must become large. As a result, it is impossible to taper bristles using a conventional physical grinding method. It is well known that if bristles are tapered, flexibility is increased so that the gums of a user are protected from injury while brushing the teeth, and penetration ability of the bristles is increased, thus enhancing tooth brushing efficiency.
In conventional anchor-less toothbrushes, because a spooled filament is typically used as bristles, it is difficult to taper bristles. Therefore, instead of a method of tapering bristles, bristles made of relatively flexible nylon, for example, nylon 6, 10, and nylon 6, 12 are used, thus overcoming the above-mentioned problems. However, a nylon bristle has insufficient durability and water resistance, compared with a polyester bristle. Also, because the penetration ability of bristles, which are not tapered, is poor, tooth brushing efficiency is reduced. Furthermore, bristles made of polyester cannot be used in such a toothbrush due to excessively high stiffness.
Due to these reasons, a tapering process is required even when manufacturing toothbrushes having various setting patterns. There are bristle tapering methods as follow. As described above, there is a method wherein a bundle of bristles is cut to a predetermined length and, thereafter, the ends of the bristles are hydrolyzed by an alkali chemical or strong acid chemical, thus being tapered. Subsequently, the bristles are washed in water and dried. Thereafter, the dried bristles are folded in half and set in a toothbrush body using anchors. There is a second method wherein bristles are tapered by a physical method such as a grinding method after a bristle setting process is conducted. There is a third method wherein bristles are partially tapered by the first method and then additionally machined by the second method.
However the second method is problematic because the length of tapered portions of the bristles is relatively short, such that the bristles are not sufficiently flexible. On the other hand, the third method has the advantages of solving the problem of the method the second method and reducing the manufacturing costs. This method was proposed in Korean Patent No. 261658 which was filed by the inventor of the present invention.
In addition, as proposed in Japanese Patent No. 3022762, there is a method wherein bristles are are immersed in an alkali chemical unit just before the cores of the bristles are dissolved, thus tapering ends of the bristles, after bristles are fastened to a toothbrush body using anchors made of metal, particularly, aluminum.
However, this method is problematic because the alkali chemical penetrates to the anchors due to a capillary phenomenon during the bristle immersion process. Thus, the anchors may be undesirably dissolved. If the anchors are dissolved, the set bristles may be removed from the toothbrush body. Furthermore, in the case of a mass production process, because hydrogen gas is generated when aluminum anchors react with alkali, there is the probability of the explosion of gas due to the heat in a reaction flask. Even if the material of the anchor is changed into brass, which has been popular, dissolution may occur because zinc, added to increase the stiffness of brass, react with alkali chemical.
Due to these reasons, a product manufactured by this method has been not commercialized. In consideration of economical efficiency, only products, which are manufactured by the method in which bristles are cut to predetermined lengths, both ends of the bristles are tapered using a chemical, and the bristles are folded in half and set in toothbrush bodies using anchors, have been commercialized.
Furthermore, in a toothbrush manufactured by this method, the thickness of an end point of each bristle is 50% or more than the thickness of the end point of the bristle before chemical-treating the bristle, and the tapered portion of the bristle is only about 3 mm. Therefore, penetration ability into gaps between teeth and flexibility are limited. To solve these problems, in Korean Patent No. 261658 which was filed by the inventor of the present invention, bristles are immersed in a chemical until just before the length of the bristles is reduced, thus being partially tapered. Thereafter, the bristles are set in a toothbrush body, and the bristles are ground by a grinder such that the diameter of an end of each bristle ranges from 0.04 mm to 0.08 mm. This method can solve problems of dissolution of an anchor and of a lack of penetration ability and flexibility.
However, the bristle tapering techniques, which are disclosed in the above-mentioned prior art, such as the conventional art proposed by the inventor of the present invention, have common problems. For example, the techniques cannot be applied to a toothbrush having variously shaped setting rows.
In an effort to overcome the above-mentioned problems, another technique was proposed in Korean Patent No. 3073200 which was filed by the inventor of the present invention. Unlike prior art using double-ended needle-shaped bristles, both ends of which are tapered, this technique uses single-ended needle-shaped bristles, only one end of which is tapered. The length of each single-ended needle-shaped bristle is half the length of the double-ended needle-shaped bristle. To manufacture a toothbrush, single-ended needle-shaped bristles are received in a receiving unit and are then inserted into a head insert, in which through holes having predetermined shapes are formed, by an insert rod of a pushing plate. Thereafter, portions of bristles protruding from a back surface of the head insert are thermally welded, thus fastening the bristles to the head insert. Subsequently, the head insert having the bristles is bonded to a toothbrush body. Alternatively, after the head insert is placed in a mold, an injection molding process is conducted, thus integrating the head insert with the toothbrush body.
In this technique, the bristles are reliably fastened to the toothbrush body without an anchor. Furthermore, because only one end of each bristle is tapered, the defective proportion is markedly low, thereby the manufacturing costs are also reduced. As well, this technique can manufacture toothbrushes having variously shaped setting rows.
However, there are problems as follows. As a first problem, in this technique, a bundle of bristles is cut to a length ranging from 15 to 20 mm and chemical-treated such that the length of tapered portions of bristles ranges from 4 to 8 mm and the thickness of end points of the bristles ranges from 0.01 to 0.03 mm. Thereafter, the bristles are tied with an elastic band after washing in water and drying them. Subsequently, the bristles are set in a bristle supply machine before a bristle setting process is conducted. At this time, some bristles may be broken due to their short lengths while removing the elastic band. Thus, the loss of bristles is increased. As a second problem, because the end point of the bristles have low thickness ranging from 0.01 to 0.03 mm, when the bristles are set in through holes of the head insert by the insert rod, the ends of the bristles may be undesirably bent. As a result, heights of the set bristles are uneven. As a third problem, the surface area of tapered bristles differs from the surface area of bristles which are not tapered. Accordingly, even for a skilled worker, much labor is required when setting the bristles in the toothbrush body.